This invention relates to the circulation of heat transfer liquids in solar heat collection and storage systems and other liquid heating devices particularly those where the source of heat is not easily interrupted when the source of power used to circulate the heat transfer liquid is interrupted.
It is common with most solar heat collecting systems which operate with liquids as the heat transfer medium that a pump, usually electrically powered, is used to move the fluid. The disadvantages of this method of circulating the liquid are listed below:
1. power must be provided from outside which is usually costly, sometimes unreliable and in many locations unavailable;
2. a motor and pump must be provided which require capital outlay, periodic maintenance, and replacement when worn out or neglected;
3. motor and pump noises are usually objectionable;
4. temperature sensing switches must be used to start and stop the circulating pump; and
5. power source interruption and/or equipment failure make certain safety devices and/or shut down facilities necessary because the source of heat, whether sun or fossil fuel, continues to put energy into the system. These devices and facilities add to initial cost and are in themselves potential sources of failure resulting in danger.
In warmer climates the storage tank and heat exchanger or solar water devices are located above the level of the collector to make use of convection forces to induce circulation and avoiding the need for circulating pumps. In colder climates there are seldom insulated parts of building higher than the solar collector where a storage tank can be placed. For purposes of solar space heating the size of the tanks required to allow for relatively long periods of no sun would dictate an expensive support structure. It has therefore become common practice to provide a storage tank/heat exchanger at ground or basement level and to rely on a circulating pump and control devices to transfer the heat to it from the collector.